The use of RFID tags are quickly gaining popularity for use in the monitoring and tracking of an item. RFID technology allows a user to remotely store and retrieve data in connection with an item utilizing a small, unobtrusive tag. As an RFID tag operates in the radio frequency (RF) portion of the electromagnetic spectrum, wireless communication can occur between an RFID tag and an RFID tag reader. This type of communication is advantageous, as it precludes the need for a direct contact or line of sight connection between the tag and the reader.
Existing passive RFID readers use transmit and receive in a single reader, primarily because the range of passive RFID is not very far, e.g. 10-20 ft. Existing battery assisted passive (BAP) RFID readers are built similarly, but need good isolation between the transmit antenna and the receive antenna to minimize leakage of the transmitting antenna back into the receiver. For example, some readers require about 40 dB of isolation between transmit and receive antennas, to get good range. This amount of isolation typically requires that the transmit and receive antennas of the reader be placed far away from each other, or requires use of directional gain pointing in the same direction which reduces the coupling between antennas by being far enough down the beamwidth of the antenna. This directional nature of the antennas also means that each pair of antenna can only cover a section of the area adjacent to the reader, e.g. a 90 degree arc pointing away from its position. To cover an entire 360 degree angle, multiple pairs of antennas are required per reader, e.g. 4 pairs of 90 degree antennas. This adds cost by requiring multiple RF ports on the reader, multiple antennas, multiple coax cables, multiple mounting brackets, and long installation times.